/Engine/Source/Runtime/GeometryCore/Public/DynamicMesh/DynamicMeshOverlay.h
If the triangle is set to valid element indices, return the indices in TriangleOut and return true, otherwise return false
bool GetTriangleIfValid ( int TriangleID, [FIndex3i](API\Runtime\GeometryCore\FIndex3i) & TriangleOut ) const